Effect of vitamin D supplementation on free and total vitamin D: a comparison of Asians vs Caucasians

OBJECTIVES: It is well established that UK Asians typically have lower vitamin D levels than Caucasians. It is also known that vitamin D binding protein (DBP) is lower in some races than Caucasians. To investigate how ethnicity, skin colour and genetic variation affect the response to vitamin D (150,000 IU) administered to young Asian and Caucasian men. DESIGN: Prospective, single centre clinical trial PARTICIPANTS: Sixty young men (18-25yr) of Asian (n=30) and Caucasian (n =30) origin MEASUREMENTS: We measured serum calcium, phosphate, magnesium, alkaline phosphatase, albumin, parathyroid hormone; total 25 hydroxyvitamin D (25OHD); calculated and directly measured free 25OHD; DBP at baseline and 4 weeks; DBP genotype, skin colour (Fitzpatrick scale), dietary vitamin D and calcium intake at baseline; and urine calcium:creatinine ratio at baseline, 1 and 4 weeks. RESULTS: At baseline, Asians had lower serum total 25OHD (26.4 [13.7] vs 34.1 [12.3] nmol/l p=0.0272) and DBP (6.7 [3.4] vs 9.6 [4.4] nmol/l; p=0.0065) but similar free 25OHD (16.7 [10.4] vs 17.8 [7.5] pmol/l p=0.6530). After dosing, total 25OHD rose similarly in each group (≈56 nmol/l), but measured free 25OHD rose more in Asians (18.1 [9.4] vs 12.2 [13.3] pmol/L p=0.0464). Lower DBP at baseline, possibly reflecting genotype differences, was associated with a greater change in measured free 25OHD in Caucasians, but not in Asians. CONCLUSIONS: Asian compared with Caucasian males had a larger increment in measured free 25OHD following 150,000 units vitamin D3, possibly reflecting differences in DBP affinity for 25OHD. Ethnicity should be considered when devising guidelines for the treatment of vitamin D deficiency. This article is protected by copyright. All rights reserved.